This invention relates to the field of alkali silicates and their use in detergent formulations. More particularly, it relates to the modification of the solubility characteristics of alkali silicates to make the alkali silicates more useful in detergent formulations.
Alkali silicates have been widely used in laundry detergents for many years. In addition to providing alkalinity and buffering, alkali silicates are important as corrosion inhibitors and process aids that improve the bead strength of detergent powders. Recent developments such as the reduction in the amount of phosphates in detergents; increased use of surfactants with unique properties; and the higher cost of energy, which affects household washing temperatures as well as the cost of manufacturing detergents by spray drying have compelled many changes in detergent formulations.
However, because of the nature of detergents as complex mixtures of ingredients, changing one component or process method can generate several new problems. In particular, the use of zeolites in detergents to replace all or part of the phosphates in formulations also containing alkali silicates has produced agglomerates that deposit on the fabric being laundered and are especially noticeable as white particulate material on dark fabrics. It has been suggested that the zeolite agglomeration results from the interaction of the zeolite with other detergent ingredients during the spray drying process.
Alkali silicates have been implicated as a component of detergents that may interact with zeolites to bind particles together and form nondispersible agglomerates. Consequently, it has been proposed that only limited amounts of silicate, 3% or less, should be used in zeolite built laundry detergents. Moreover, larger amounts of alkali silicates have been reported to decrease the ion exchange capacity and the rate of ion exchange of the zeolites in a formulated detergent. However, reducing the amount or eliminating alkali silicates in detergent formulations is not a satisfactory solution because it results in the loss or reduction of the valuable properties such as bead formation and anticorrosion that the silicate provides.
U.S. Pat. Nos. 4,138,363, 4,216,125 and 4,243,545 teach that the tendency of zeolites to agglomerate during detergent processing can be reduced by treating the zeolite surface with a hydrophilic functional silane. While acrylates, epoxies, amines and carboxylates are suggested as useful hydrophilic groups, the only silanes taught for treating the zeolite were beta-3,4-epoxycyclohexyl-ethyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane and gamma-aminopropyltrimethoxysilane. However, the improvement achieved with these silane-zeolite composites has not been sufficient to result in commercial utilization.
Consequently there is still a need for a commercially viable way of making alkali silicates and zeolites compatible in detergent formulations. Accordingly, it is a purpose of the present invention to provide a method of modifying the solubility characteristics of alkali silicate so that alkali silicate solids and binder films present in detergent powders are more rapidly and readily resolubilized in water. Similarly, it is a purpose of this invention to provide detergent compositions containing a solubility-modified silicate ingredient. It is also an object of the invention to provide detergent compositions that are more rapidly and homogeneously soluble in water. Such detergent powders could be packaged, stored and shipped more economically and still be easy to use because of their rapid solubilization in water.
U.S. Pat. No. 4,157,978 teaches that multimeric silicates can be "capped" by aluminum diacetate groups and incorporated in spray dried detergent compositions to provide an overall improvement in the physical characteristics and rate of solubility of the resulting detergent granules. The patent also suggests that other "capped" silicate materials known in the art can be used in detergent formulations. As an example of such other "capped" silicates, the patent describes silicates "capped" by triorganosilyl groups.
Mixtures of alkali silicates and certain organofunctional siliconates have been prepared in aqueous solutions and have been found useful as corrosion inhibitors in antifreeze compositions for automotive cooling systems. The mixtures are generally considered to form copolymers in which the organofunctional siliconate units act to stabilize the silicate units in aqueous solutions. Specifically, the copolymer remains in solution under conditions of pH and concentration that result in the separation of gels or precipitates when alkali silicates are employed alone.
Siliconates with several types of organofunctional substituents have been found especially useful for stabilizing alkali silicates by formation of copolymers. For example, U.S. Pat. No. 3,198,820 teaches the use of siliconates with alkali carboxylate functional organic substituents; U.S. Pat. Nos. 4,352,742, 4,354,002, and 4,362,644 teach the use of siliconates with alkali sulfonate functional organic substituents; U.S. Pat. Nos. 4,370,255 and 4,333,843 teach the use of siliconates with alkali phosphonate functional organic substituents; U.S. Pat. No. 4,344,860 teaches the use of siliconates with sulfur or nitrogen containing alkali carboxylate functional organic substitutents; and U.S. Pat. No. 4,503,242 teaches the use of siliconates with amine containing alkali sulfonate functional organic substituents.
The siliconate-silicate references are all concerned with keeping alkali silicates in solution, especially in alcoholic antifreeze solutions.